Some question whether God has forbidden contact with the dead, based on Deuteronomy 18: 10-11. This, however, is obviously untrue as he has at times permitted it, as when Moses and Elijah appear to Christ. What was forbidden necromantic practices (Deut. 18: 10-15).
We are not to conjure the dead to gain information (I think both Catholics and Protestants can agree on this one!). But I think it’s quite easy to see that asking for prayers and conjuring the dead are completely different things. One is a humble request for prayer, the other is a coercive occult practice.
Now to answer the point “omniscient like God.” As unglorified mortals we do indeed suffer many restrictions, as we are inside of time. But the Church Militant, that is, those of us here on Earth, are not the only members of the Church that exist. Saints are the Church Triumphant (just as those in purgatory are the Church Suffering) and they are not bound by space and time and the limitations associated with them.
I am not suggesting that the saints are omniscient, as God is, only that they are not bound by space and time as we are. Now since we’ve already established scripturally that they can hear our prayers and that their intercession is pleasing to God, I think I’ve covered most of the points that come up.
But I still have one more post!